The use of telecommunications (TK) services, for example telephoning, telefaxing, access to data base systems and such, is not as a rule without cost for the user, but is charged to the customer by the service provider by means of rate-based fees. In addition to fixed basic charges, most bills also contain usage-dependent amounts of fees for the use of chargeable services, where the latter often make up the lion's share of the bill. The usual way of rating in telecommunications is described for example in the "Textbook of Telecommunications" volume 1, Technical Publishers Schiele & Schon GmbH, Berlin 1986, pages 614 to 620.
Usually the fee structures for determining the charges are relatively rigid and only differ from each other in distance zones and times of day. In most cases discounts are offered for sundays and holidays, as opposed to working days. But in principle most cases provide the same charging structure for every user of the respective TK services.
Concepts of individual subscriber rating have been introduced lately to increase the incentive of using a certain TK service, whereby for example connections of a user to other TK terminals in the telephone area, which can be individually established for the respective subscriber (represented by the corresponding telephone numbers) are billed at a more favorable rate.